Back draft damper for exhaust fans



Aug. 31, 1954 c. PRUDHON BACK DRAFT DAMPER FOR EXHAUST FANS Filed 001;. 27, 1951 hwy Clark Frudimn Patented Aug. 31, 1954.

UNITED STATES PATENT 2,687,687 7 FOR EXHAUST FANS BACK DRAFT DAMPER Clark Prudhon, Fort Pruden Products 1 Claim.

This invention relates to ventilating apparatus and refers more particularly to a back draft damper for exhaust fans and the like.

of the type to which this inventhe flow of when it is OFFICE Atkinson, Wis., assignor to (30., Fort corporation of Wisconsin Application October 27,

Atkinson, Wis., a

1951, Serial No. 253,493 (Cl. 98-116) application of the principles thereof, and in which: t

Figure 1 is a sectional side view of an exhaust fan having the back draft damper of this invention of the damper of this invention'installed in the outlet duct of an exhaust fan and shown in closed position. l i l Referring now more particularly to the accompanying drawing, in which like numerals designate like parts throughout the several views, the

of pitched blades to the motor shaft.

The motor is of course connected by means of onductors It) to a suitable source of electric The fan is mounted in a housing II which comprises a duct I2 having the back draft damper I3 of this invention installed therein. This housing, which is normally fabricated of mounted at the interior of the housing by having its motor secured to a pair of duct l2.

A suitable hood l7, secured to the outside of the building, shelters the outlet of the exhaust protect the duct opening from rain and snow, particularly in severe weather during intervals when the fan is not fan is turned ofi.

This damper comprises a pair of flat semicircular wings |8 mounted with their straight edges vertical and other and in a manner permitting them to swing freely, flatwise, toward and from a closed position in which they are coplanar. A rod 20 is flatwise secured to each of the wings, near its straight edge and nearly, but not exactly, parallel thereto. The curved edges of the wings are notched adjacent their straight edges, as at 2|, so that the ends of the rods project beyond the wings to provide trunnions, said projecting ends of the rods being journaled in suitable holes in brackets 22 and 23 secured to the top and bottom of the duct l2, near the outlet thereof. The lower bracket 23 has its outer end portion ofiset upwardly, and the rounded lower ends of the rods ride on the upper surface of an arm 24 which is fastened between the inner end of the lower bracket and the duct. The arm 24 thus provides a relatively frictionless bearing support for the rods to enable the wings to swing freely.

The bearing holes in the brackets 22 and 23 are so disposed with respect to one another and the rods that the force of gravity will at all times act upon the wings to swing them inwardly toward their coplanar or'closed position. More specifically, the two rods are disposed in a common plane substantially transverse to the duct axis (corresponding to the plane of the wings in their closed position), which plane, however, is tilted inwardly, toward the fan rotor, at its top, as shown in Figure 1. Moreover, the two rods converge downwardly toward one another, as well as toward the adjacent straight edges of their respective wings, as shown in Figure 2. The rods-and hence the pivot axes of the wings-are thus offset from the vertical in two directions, with the result that the wings will at all times tend to swing inwardly toward the fan rotor.

The outlet end of the duct is provided with a rolled lip 25 which provides an abutment against which the marginal edge portions of the wings engage in their coplanar closed position and which prevents them from swinging forwardly of said closed position. From this closed position the wings may be readily swung outwardly, to an open position, by the force of the stream of exhaust air expelled by the fan rotor when the fan is operating.

From the foregoing description, taken together with the accompanying drawing, it will be readily apparent that this invention provides an automatic back draft damper for an exhaust fan of the character described, which damper will close the outlet duct of the fan when the fan is .not operating and will swing to an open position whenever the fan works. It will also be apparent that the automatic check valve effect of the damper of this invention is achieved by reason of the fact that the pivot axes of the two wings which comprise the damper are offset from the vertical so that each of said wings will at all times tend to swing forwardly toward the fan rotor.

I claim:

A back draft damper for automatically closing an air duct downstream of an exhaust fan or the like when the fan is not operating, comprising: a pair of flat damper wings, each having substantially the shape of one-half of the duct cross section and said wings having straight edges adapted to lie closely adjacent to one another when the wings are disposed in coplanar positionclosing the duct; a straight rod flatwise overlying and secured to each of said wings near its said straight edge and having its upper and lower end portions projecting beyond the wing to provide trunnions, said rod converging downwardly toward said straight edge; and means freely pivotally mounting the wings in the duct, said means including a bracket at the bottom of the duct having apertures in which the lower trunnions are journaled and apertured means at the top of the duct in which the upper trunnions are journaled, the upper and lower apertures in which each rod is journaled being so disposed that the axes of the two rods lie in a common, nearly vertical plane substantially transverse to the duct axis, said plane being displaced from the vertical by having its top closer to the fan, and said axes being displaced from the vertical within said plane by diverging {upwardly so that said wings will at all times tend to swing by gravity towards a position in which they are coplanar to thus substantially close the duct in said coplanar position; but so that said wings may be swung into alignment with the air stream from the fan by the force of said air stream.

References Cited in the file of this patent UNITED STATES PATENTS 

